Intrastate and Interstate Water Transfers

Riparian states generally do not permit transfers of water outside the watershed of origin, while the opposite is true in the appropriation states provided there is no harm to existing appropriators. The three mechanisms utilized to apportion interstate water are interstate compacts approved by Congress, judicial allocation and legislative allocation. Interstate litigation results when states have failed to negotiate an apportionment among themselves. Courts use a judicial decree to allocate the disputed interstate water among contesting states by applying the 'equitable apportionment' doctrine. Congressional apportionment has been used once to apportion water in the lower Colorado River basin. The federal government may preempt existing state control over water rights for matters concerning interstate commerce, navigation and the development of federal projects.